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Offline OutdoorAdv

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Cracked Aluminum Exhaust Bracket
« on: October 06, 2018, 07:23:31 PM »
Has anyone ever had any cracks on the Mokai CNC made anodized aluminum exhaust bracket?  The bracket that comes off the block and secures the muffler assembly.  Sorry, no pictures on this post, I am currently without a phone.  I pulled my engine today to clean the boat and noticed two of the aluminum arms on that bracket are broken.  Then, when I took the muffler off I also noticed that the SS brace that goes from the tailpipe section to the allen screw is also broken off at the tailpipe under the wrap.

It appears to be a result of the vibration between the muffler section and the header pipe.  The header pipe is not a tight fit into the muffler on my engine and with the silicone washers, its allowing about 1/32nd to 1/16th of vibration play with the muffler section.  That aluminum bracket also flexes quite a bit and really should have been made a bit sturdier.  Glad I noticed it before the rest of the aluminum bracket failed and let the hot muffler fall off into the engine compartment while on the water!!

I'm going to TIG weld the breaks, and fix the issues with the amount of play between the header and muffler.  I just wanted to see if anyone else has had this issue.

Offline Painlesstom

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Re: Cracked Aluminum Exhaust Bracket
« Reply #1 on: October 06, 2018, 08:16:36 PM »
I haven't heard of any others breaking yet, you might be the one person who's used an ES-kape long enough to encounter that problem. I wouldn't bother fixing that bracket, would suggest making one from steel instead. If I was going to use the stock exhaust I would weld it so it was one piece and get rid of the dampening washers in the mount, instead making it solid. All the ES-kapes had sloppy fit exhaust unions, makes for more noise and leaks that contribute to the backfiring at shutdown. The design shouldn't have gone past prototyping.
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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #2 on: October 07, 2018, 12:33:04 AM »
I haven't heard of any others breaking yet, you might be the one person who's used an ES-kape long enough to encounter that problem. I wouldn't bother fixing that bracket, would suggest making one from steel instead. If I was going to use the stock exhaust I would weld it so it was one piece and get rid of the dampening washers in the mount, instead making it solid. All the ES-kapes had sloppy fit exhaust unions, makes for more noise and leaks that contribute to the backfiring at shutdown. The design shouldn't have gone past prototyping.

Great info man, and a great idea... I have some 1/8th and/or 3/16th steel plate I could easily make a new bracket from.  Ever since I did the true cold air intake, I have the afterfire\backfire at shutdown... when I pull up to a crowded ramp, I'll often choke the motor to make it rich before cutting the ignition so I don't scare people.  It never occurred to me that it could be caused by the sloppy exhaust fit... My theory was after the cold air intake switch, the carb is not fighting a vacuum and was running more lean with free flowing air, causing a lean environment at shutdown and the afterfire.  Do you know if Mokai jetted the carbs to account for the stock plenum vacuum?  Now I'm thinking this issue could be air coming into the hot exhaust at shutdown.  It'd be great to resolve that afterfire\backfire too.

I should have a new phone in a week or two and ill put some pictures on here of the breaks, just in case it can help someone in the future.  I think I'll TIG them together for a quick fix now and as you suggested, cut a new bracket out of some plate this winter and scrap the silicone washers with some bar stock out to the muffler mounts off the new bracket.

My thoughts on fixing the sloppy fit between the header pipe and muffler would be 1) weld the header to the muffler, 2) slot the muffler sleeve and clamp it to the header or 3) weld SS studs on the header and muffler with a bracket between just like the muffler to tailpipe connection.  Any thoughts on which might be the best solution??  The easiest is just to weld them together... but before I do, I'm trying to think of reasons why I might need to take them apart in the future. 

Thanks a ton for the info and feedback Tom,
    Brad

Offline Painlesstom

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Re: Cracked Aluminum Exhaust Bracket
« Reply #3 on: October 07, 2018, 04:18:12 PM »
The backfire is caused by residual fuel and a hot muffler with an air leak. The fuel comes from the governor system opening the throttle during shutdown. If you unhook the long thin spring that rides the throttle linkage rod to the carburetor your idle will be more consistent and it will stay at idle when you shut down, the backfire goes away completely. Side effect would be the need to crack the throttle a little to start, more so when cold, not a big deal.

You could slot the muffler ends, wrap the header and outlet pipe with something to act as a bushing/gasket, and clamp the joints. That would reduce the chance of stress cracks and quiet things down. Personally I would make the mounting posts rigid and weld the whole exhaust together, you could still take the top mount screws loose and remove the header bolts to remove the whole assembly. It's not as nice as my water cooled muffler but it's tolerable.

Look forward to seeing what you do. Please keep us posted.  \./8
Tom

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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #4 on: October 07, 2018, 07:00:04 PM »
Thanks a ton for the advice Tom.  I can't tell ya how excited I am get get rid of that damn afterfire/backfire!  I am going to patch this together for now to get me through the rest of the season.  This winter I will properly address the exhaust system.  If I remake that bracket, I am going to do it with SS plate, so I'll need to pick some up next time I'm at the steel supplier.  I will absolutely update this thread with pictures of the broken brackets and whatever solution I do to address it.

I am leaning towards TIG welding the header, muffler and tailpipe into one piece and like you said, removing the header bolts if I ever need to take the exhaust off.  The only downside to that is those pieces are all custom and I am sure if I ever had an issue and needed a new piece of the exhaust system, it would cost me a small fortune from Mokai!!  So I may think on it for a bit and may slot and clamp with a bushing material.  I bet fixing those exhaust leaks and vibrations is really going to quiet everything down. 

Thanks again Tom.

Offline Painlesstom

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Re: Cracked Aluminum Exhaust Bracket
« Reply #5 on: October 07, 2018, 08:15:07 PM »
I have a some stock ES-kape exhaust parts from converting boats to my muffler, so if you ever needed something I would make you a deal you could live with easily. lol  ;)

Glad to help!  :)
Tom

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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #6 on: October 07, 2018, 08:57:27 PM »
I have a some stock ES-kape exhaust parts from converting boats to my muffler, so if you ever needed something I would make you a deal you could live with easily. lol  ;)

Glad to help!  :)

Awesome!  That just made the decision super easy... I'm going to just weld the exhaust into one solid piece then.  Makes me feel better knowing there's a reasonable source of exhaust parts in the future if I were to ever need something.

Thanks again Tom.

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Re: Cracked Aluminum Exhaust Bracket
« Reply #7 on: October 07, 2018, 09:00:56 PM »
 :) ;) :)
Tom

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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #8 on: October 09, 2018, 03:04:31 PM »
Here are the cracks\breaks.  I had already started cleaning them up to fix them.  I'll finish prepping and get it all welded up this evening.  I didn't have enough wrap here, so I ordered some good stuff and it'll be in Thurs, so I'll have it back on the water this weekend.  My plan for now it to fix the breaks in the aluminum, weld the SS bracket back on and weld the SS header to the muffler to fix the sloppy fit wobble that caused this in the first place.  That should also fix the exhaust leaks.  For now, I'm not welding the tailpipe to the muffler, but I did order some Permatex muffler\tailpipe sealer that I will try in the space there.  That is a much tighter fit on that side and has the bracket that keeps that joint stationary, so the sealer should stay in place, especially with wrap over it.  If it doesn't, I'll weld that joint this winter as well.

This winter I might scrap the aluminum bracket and fabricate a new one out of SS.  I'm a bit of a perfectionist and I dont have the time to mess with that now while there is still nice boatable weather outside.

Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #9 on: October 09, 2018, 06:06:28 PM »
Its all welded back together!  One of the broken aluminum arms welded fine, but the other I couldn't get a good puddle no matter what I tried.  Its good enough for now though, but I will for sure be making a new bracket out of SS plate this winter.  With the exhaust welded together it is SOLID with no where near as much wobbling.  Once the new header wrap gets here thurs it'll be back in service.  I'll get some pictures when its done.

Offline Painlesstom

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Re: Cracked Aluminum Exhaust Bracket
« Reply #10 on: October 09, 2018, 06:49:53 PM »
Cool, sounds like it will be a suitable temp fix. Just keep an eye on it as I'm sure you will.  \./8
Tom

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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #11 on: October 09, 2018, 07:33:07 PM »
Thanks Tom.  Now that the muffler is welded to the header, I'm not as concerned about it.  If that aluminum bracket cracks again on me before I can replace it, I at least feel better knowing the hot muffler wont fall into the engine compartment and melt stuff. ha  I'm excited to see if the backfire issue is fixed.

Offline Painlesstom

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Re: Cracked Aluminum Exhaust Bracket
« Reply #12 on: October 09, 2018, 07:39:02 PM »
The leak between the muffler and header was only one contributing factor to the backfire, the spring I mentioned on the linkage rod is the main cause.
Tom

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Offline OutdoorAdv

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Re: Cracked Aluminum Exhaust Bracket
« Reply #13 on: October 11, 2018, 11:45:08 AM »
I still don't have a phone, so its a pain to get pictures right now.  I was able to take a few while I was putting it back together.  The whole exhaust is SOLID now with the muffler welded to the header.  I don't think I'll have any other issues with vibrations causing stress cracks, however I am making the aluminum bracket out of SS this weekend.  I'm just not happy with how one of the arms welded back together.  New wrap is on, with 304 SS bands.  There are no leaks in the exhaust now, so I'm hopeful for a noise reduction... or at least a more mellow tone while running.

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Re: Cracked Aluminum Exhaust Bracket
« Reply #14 on: October 11, 2018, 12:00:00 PM »
Will be quieter for sure. The spring is circled in the pic, pop it loose from the governor arm to stop backfiring.
Tom

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